Semiconductor devices are typically manufactured in large numbers on a semiconductor wafer. For various reasons, semiconductor devices may fail to perform correctly. Accordingly, as a part of the manufacturing process, various tests of the semiconductor devices are typically performed. Tests can include, for example, functional tests, speed tests and sorting, and burn-in testing. Testing can be performed of a wafer (e.g., before the semiconductor devices are separated from each other by a process called singulation), or of individual semiconductor devices (e.g., held in a carrier after singulation). Making temporary electrical connections to the semiconductor devices to pass test signals to and from the devices can be accomplished using a probe card assembly.
For example, a probe card assembly can include many probes that are arranged to make temporary pressure-based electrical contacts to corresponding terminals (e.g., aluminum bond pads) on the semiconductor devices. A minimum amount of probe contact force can be desirable in order to reliably break through non-conductive oxide layers which can form on some kinds of terminals. Sometimes, it can also be desirable to provide a scrubbing action of the probe relative to the terminal to assist in breaking through the oxide layer.
While a minimum amount of probe contact force can generally necessary, providing too much force can be undesirable. Excessive force can result in probes being broken or damaged (e.g., permanently bent). Excessive force or excessive scrubbing action can also result in damage to the terminal (e.g., large scrub marks, cracked terminals, etc.). Accordingly, it can be difficult to provide a proper balance between providing enough force to provide a reliable electrical contact and not so much force that the probe or terminal is damaged.
With continuing trend towards larger wafers and larger numbers of interconnects, the above-mentioned challenges become even greater. As probe card assemblies become larger, it can be more difficult to provide probes which are aligned with each other in a common plane. Alignment between the probe card assembly and wafer under test also becomes more challenging. Errors in planarity or alignment can result in excessively high forces on some probes and inadequate forces on other probes.
Managing contact forces on a probe card assembly having many thousands of probes can be challenging. In order to accommodate some misalignment, probes can be made to provide a spring-like character. In use, the probe card can be brought into contact with the wafer under test, and then the probe card and wafer pushed further together by a distance referred to as over travel. Providing probes enough over travel to ensure that all probes make reliable contact can be difficult. Increasing the amount of over travel can also present problems, as this increases the force on the probes. As noted above, increased forces can result in damage to the probes or terminals of the semiconductor devices.
As the number of contacts increases, the total force applied to the probe card assembly also increases in proportion to the number of probes. These high forces can be difficult to manage, as they can bend or warp the probe card assembly itself, aggravating alignment and non-planarity challenges.